Hello,

I am making some test with VOPSOP.

For that I created a sphere. I attached a VOPSOP to.
I tried to put the Normal output from the Global Variables node to the Velocity of the Output node and …. Nothing.
I was expecting the sphere start growing …
In fact I can put anything on the Velocity of the Output node, my sphere mesh doesn't change a bit.

Can someone tell me why ?

Thanks for you help

What you're doing with you VOPSOP is just creating an attribute Velocity.
If you want to modify your sphere based on that, you need to use this attribute to do whatever you want to do.

e.g. See attached file.
As you did, I'm creating a sphere, setting the normals and setting the velocity based on the normal value. Then I'm using a PointSOP to update the point position based on the current frame and the velocity value.
Press play.

Hopefully that will make sense.

hmm … It makes sense ( a lot !) Thx

I was hoping to get time dependent Vopsop this way. But it seems I am all wrong

Is there a way to deal with time Within a VopSop ?
Do I need a VopPop do to that ? If I put some vector in the Velocity Input of a VopPop… things happens !

How Is it possible to transfert particle position to pointmesh position?


Thanks again.

vbk!!!
hmm … It makes sense ( a lot !) Thx

I was hoping to get time dependent Vopsop this way. But it seems I am all wrong

How so? The attached example file shows explicitly how to use time in the result. It is in a Point SOP expression but you can do the same in VOPs.

vbk!!!
Is there a way to deal with time Within a VopSop ?
Do I need a VopPop do to that ? If I put some vector in the Velocity Input of a VopPop… things happens !

Yes.
Best to use a parameter with either $T, $F or $FF in it as you won't be recompiling the VOP network every frame.

If you decide to use $T, $F or $FF in a constant or in a parameter field directly inside VOPs/VEX, then you will force the VOP network to recompile every frame. Not so good.

Either way you can most certainly incorporate time how ever you wish in VOPs. Couple that with the Time Shift SOP as an input and you can even run your vop network across time with time.

vbk!!!
How Is it possible to transfert particle position to pointmesh position?

May ways to do this and it all depends on the situation.

If you can ensure that the two topologies are like, then you can use a Point SOP's second input to map/mix it in. For example if you want to use the second input's position to the first, you can use this in the position parameters:
$TX2 $TY2 $TZ2

You can also do the same in VOPs. Use the Import Attribute to bring in P using the input index set to 2. There is the ever so convenient Mix VOP to mix in any two attributes based on a bias parameter which could be any float value.

If your two topologies are different, you are birthing particles right? So make sure to birth your particles and pick up some attribute on your source geometry that meshes with your target geometry. The “rest” attribute (Rest SOP) as a static position on your source birthing geometry comes in handy. That way you can always move your particles to their rest attribute position, mix in your results and then reapply the current particle position.


So many ways to do this and with such a vague question and response, who knows what you want…

I am trying to make Vopsop Collision using Volume Gradient.
I works not that bad …
I use the Displacement node to create Normal displacement of some specific points.
Now I would like :
- to add some delay when the mesh come back to the rest position.
- to add secondary displacement around the border of the displaced points to fake some volume conservation behavior.

For the second task, I made some progress.
Is there a way to calculate the volume of a mesh easily in Houdini ? My plan is to use that to “control” the displacement's amount.

For the first task, I began to ask you some question about it …
I will ask you more soon I guess.

++

Vincent

ok

I finished my secondary displacement Vopsop.
http://vimeo.com/22882649 [vimeo.com]

Now I have to think about the including a delay to the deformation.


++

Very nice. I really like the control around the edge of the deformation.

vbk!!!
…
- to add some delay when the mesh come back to the rest position.
…

you need to use SopSolver DOP, it's quite easy to use, there is lot of info on the forums about it
just blend current geometry towards rest geometry a little each frame

vbk!!!
…
Is there a way to calculate the volume of a mesh easily in Houdini ? My plan is to use that to “control” the displacement's amount.
…

measure SOP in volume mode
then Attribute Promote volume attribute from primitive to detail by Sum to get the volume of the whole closed mesh

thanks a lot Tomas

I will take some info about the Sopsolver DOP

About the volume I use the bouding box volume to control my secondary displacement. I created an attribute from that. It s not accurate but It works for now !


++

Vincent

hello all,

I tried the Sopsolver but don't understand how to use it properlly to achieve my effect.
I am trying to make the lag within CHOP now and I have a problem ( again ).
If you look at the picture attached, You can see a channel coming from a geometry ( called voldiff). What I would like is my lag only react when the value of voldiff is under or equal to zero.

How It could be possbile in CHOP ?

Thanks for your help.

++

Vincent

edit: there is a picture now …